Well, if we didn't have plenty of rookies each year we'd eventually run out of drivers
There's also the complication of different teams getting an entry each year and thus either the team owner or his contracted drivers being new.
A percentage would be better rather than a straight number, yes, I know for the past few years it's been 3 drivers per car, but wasn't last year the first year to go back to 55 cars after 53, and way back in the 90's it wasn't always a full grid was it?
So it's all a bit "Lies, Damm Lies & Statistics" isn't it?